I work at an MSP who has an existing customer.
They want _one_ company to handle all their IT needs. They have a server in a datacenter that runs an important application and it doesn't use much space. We would be doing full image backups. We aren't experts in Linux but we know enough to be able to test the backups and restore the backup image into
a vm. If they
went with another company, they would get
charged 2x to 3x as much.

I looked at Datto's pricing (I don't like datto, just comparing) and they are $300 usd per month.

I figured this post would go in an MSP group, but I couldn't find one.

Do you have storage in the DC to backup to or are you wanting to go directly to the cloud? Do you have access to any other resources in the DC other servers or etc? Do you need to offsite replicate? (I would assume yes) Do you have an application layer backup for what the linux server is running could you backup to local storage then rsync the backup to a different site?

Vembu VMBackup -
Vembu VMBackup is a Backup and Disaster Recovery software that supports VMware vSphere and Microsoft Hyper-V environments. VMBackup is designed to backup and replicate the virtual machines by taking the snapshots of the VM images at the host (hypervisor) level. There is no need to install any agent on each virtual machine (guest OS). Also, during incremental backups, only changed blocks will be transferred. Application-aware image backup processing ensures application consistency with logs being truncated after successful backups. The quick vm recovery helps you to instantly launch the backed up VMs on ESXi host or Hyper-V or any other hypervisor. Costs 360$ for VMWare and 240$ for Hyper - V costs per-socket /year.

If I am not wrong you are running a physical Linux server as you mentioned restoring as a VM....if you on VM already, not so much of a concern....

If you are prepared to "restore to a VM" ? why not do the exercise and convert to VM right away as you would have many more options backing up VMs using software like Veeam where you can use reverse increment instead of 100% full backup or worry about increment backup failures.

Its also easier to create replica using Veeam, store one replica onsite and another in cloud or remote site....out of the box feature....